A catalyst comprising a mixed metal oxide is useful for vapor phase partial oxidation of alkane, alkene or a mixture of alkane and alkene to an unsaturated carboxylic acid and for vapor phase oxidation of alkane, alkene or a mixture of alkane and alkene to unsaturated nitrile in the presence of ammonia.
For the production of acrylic acid, it has been widely practiced on a commercial scale a method which adopts acrolein as a raw material and affects the vapor phase partial oxidation thereof with molecular oxygen in the presence of a catalyst. Some patent applications disclosing a catalyst used for the production of the acrylic acid through the vapor phase oxidation of acrolein have been filed. The acrolein oxidation catalyst disclosed in the applications comprises molybdenum and vanadium as main components, and components, such as tungsten, chrome, copper, potassium and the like, are added, thereby improving capability thereof. For example, Japanese Patent Publication No. 12129/69 discloses a catalyst consisting of molybdenum, vanadium and tungsten, Japanese Patent Publication No. 25914/75 discloses a catalyst consisting of molybdenum, vanadium, copper and chrome, and Japanese Unexamined Patent Publication No. 85091/77 discloses a catalyst consisting of molybdenum, vanadium, copper, and at least one component selected from antimony and germanium. In addition, European Patent No. EP-023859 discloses that although the components and composition of the catalyst are identical, the conversion rate of the acrolein and a yield of the acrylic acid are significantly varied depending upon a method of forming the catalyst, when producing the catalyst. Also, the above European Patent discloses a method for producing the catalyst which produces acrylic acid at yields of high levels.
Recently, a demand for the catalyst having more high conversion rate and yield is increased. Studies for producing the corresponding catalyst are actively proceeding.
For example, when the catalyst for partially oxidizing the acrolein to the acrylic acid comprising the mixed metal oxide is prepared, it is difficult to uniformly maintain a suspension, since the precipitate is generated by reaction of a cationic metal salt with anionic metal salt in an aqueous solution, is rapidly settled when agitation is stopped and thus is phase separated from a water layer.
When containing on the inert carrier the suspension with the phase separation, it is difficult to maintain the uniformity, causing the uniformity problem of a catalyst article whenever the catalyst is produced. Also, if a particle size of a precipitate is large, it is difficult to transfer the suspension through a pumping operation and to contain the catalyst on the carrier using nozzle injection, so that the production thereof may run into a snag. In addition, the capacity of the catalyst is remarkably dependent upon the particle size of the metal salt contained in the suspension. Preferably, these metal salts consist of particles of less than 10 microns (refer to Korean Patent Publication No. 1998-073604). Accordingly, it is required to have a method of effectively suppressing the layer separation and decreasing the particle size of the suspension.